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The Schiehallion experiment was an 18th-century experiment to determine the mean density of the Earth. Funded by a grant from the Royal Society, it was conducted in the summer of 1774 around the Scottish mountain of Schiehallion, Perthshire. The experiment involved measuring the tiny deflection of a pendulum due to the gravitational attraction of a nearby mountain. Schiehallion was considered the ideal location after a search for candidate mountains, thanks to its isolation and almost symmetrical shape. One of the triggers for the experiment were anomalies noted during the survey of the Mason–Dixon line.
A pendulum hangs straight downwards in a symmetrical gravitational field. However, if a sufficiently large mass such as a mountain is nearby, its gravitational attraction should pull the pendulum's plumb-bob slightly out of true (in the sense that it doesn't point to the centre of mass of the Earth).
If the mass of the mountain could be independently established from a determination of its volume and an estimate of the mean density of its rocks, then these values could be extrapolated to provide the mean density of the Earth, and by extension, its mass.
Nevil Maskelyne’s 1774 experiment on the Scottish mountain Schiehallion set out to derive the mean density of the Earth, from astronomical observations of the deflection of the vertical and calculation of the mountain’s relative gravitational attraction. Using Maskelyne’s results and lithological survey results, John Playfair estimated mean Earth specific gravity to be 4.56–4.87, while Charles Hutton argued in 1821 that the Earth was ‘very near five times the density of water; but not higher’. Hutton challenged future workers to identify any areas in which his analysis could be improved. The geometry of the 1774 experiment has therefore been recomputed within a digital elevation model extending 120 km from the mountain. Three contributions to the deflection of the vertical have been included: topography, and local and regional subsurface density variations. Local subsurface densities have been modelled using geological maps, cross-sections and laboratory measurements. Regional subsurface effects have been included from analysis of the Bouguer gravity anomaly. The outcome of the new modelling is to credit Maskelyne for his accurate astronomical observations, as together with the new density structure model, they yield a mean Earth density of 5480 ± 250 kgm^−3, in agreement with the modern value of 5515 kg m^−3.
Yes, I think the entire experiment was amazing for 1774 technology. I always took contour lines for granted and never even thought about how they were first invented or used.
originally posted by: sapien82
don't you think its amazing that through the task of surveying that Hutton invented contour lines
When I watched these Veritasium videos, I realized that probably most people don't understand heat versus temperature and have some misconceptions about both, so I recommend watching these if you can since they try to correct some misconceptions. Watching both will take less than 10 minutes:
originally posted by: Finspiracy
This is a really simple and basic question. I am about seem very stupid but i rather ask and learn, than stay stupid.
Google told you right, but it doesn't say it's always the same thing exactly, does it? It talks about different types of heat transfer, and even if you pick one type like conduction in solids, that transfer can vary dramatically from one type of solid to another type of solid, as demonstrated in the veritasium video, enough to throw off our perceptions of heat and temperature enough that nearly everybody gets the wrong answers to what is going on in the demonstrations. That video shows people touching a book and touching a hard drive, and the thermal conductivity of those solids is so much different that people have a hard time judging the temperatures of them by touching them. When Derek says they are the same temperature, everybody calls him a liar until he proves it using a thermometer.
Isn't heat always just heat, regardless of the heat source? Are there different kinds of heat?
Google told me that "conduction in solids, convection of fluids (liquids or gases), and radiation through anything that will allow radiation to pass. The method used to transfer heat is usually the one that is the most efficient." And that is about transfer. But the heat which is transferred is always the same thing right?
I have no idea how to explain that using physics, but if you're suggesting the answer is psychological because you prefer the beauty of nature, that would make sense.
I like sauna very much. Electric saunas don't feel as good as the ones with the wood burning stove. I have an electric heater in my sauna, stones of course, and when i throw water on the stones, the result is not as pleasant as with wood burning stoves. Sometimes i get to bathe in a wood burning stove sauna, they are usually near a lake or sea, beautiful scenery, trees, nature. So my thought has always been that heat is heat, there is one heat, and that's it, and saunas in nature, with wood burning stoves and water nearby, just make the overall experience so much more pleasant that the heat feels better there too.
originally posted by: sapien82
a reply to: Finspiracy
I think I Understand what you mean about the difference between the heat , what I think is a dry heat and heat with humidity in the air give you very different feelings in the body on your skin.
I prefer humid heat to dry heat , like the heat of a forest or jungle , compared to the heat of a desert.
And i have a long time been wondering why is that, if heat is always heat?
The reason I didn't think humidity should explain the difference between the electric sauna versus wood-burning is because the exhaust gases from burning wood, while containing water vapor, should be vented outside the sauna, so that shouldn't have an effect. So if you put water on the heated stones to create humidity, if everything else is the same, such as the type of stones, temperature of the stones, amount of water used, etc, then the amount of humidity generated from putting water on the stones should be the same either way, shouldn't it?
originally posted by: Finspiracy
Yes, this has to do with humidity too, and the heat which is stored into the material (stones this time) to create steam. All of us here are told at a very young age, that the temperature of a sauna does not increase when water is thrown on the stones, which are on the sauna stove. Like... you can be in a 100 degree (celsius) air for a while but never in a water that hot. It is the humidity that increases with water -> steam reaction. But the body sensation is heat.
And the result of that water -> steam reaction feels different in an electric sauna, when compared to a one with a wood burning stove. And i have a long time been wondering why is that, if heat is always heat?
originally posted by: Arbitrageur
So if you put water on the heated stones to create humidity, if everything else is the same, such as the type of stones, temperature of the stones, amount of water used, etc, then the amount of humidity generated from putting water on the stones should be the same either way, shouldn't it?